It is the purpose of this project to examine the movement related behavior of identified efferent cell systems within the primate motor cortex, and the manner in which this behavior changes when one of these major descending pathways is transected. Experiments are carried out with alert monkeys, who have been trained to control the position of the wrist in the presence of perturbing forces. Single unit recording methods are used at both the segmental and cortical levels to characterize the behavior of identified cells during task performance. The experiments are carried out in both normal and in recovering, tractotomized animals. The results have significance both for our understanding of the normal, cortical control of movement, and for the mechanisms underlying recovery of motor function following CNS trauma and stroke.